This invention relates generally to random access storage and retrieval systems, and more particularly to a system for rapidly and accurately accessing a selected storage location or position contained within a two dimensional array located in a storage medium.
Prior random access retrieval and storage systems are of several forms, among which is the type which utilizes a grooveless magnetic disc having a plurality of concentric discrete tracks divided into a plurality of angular sectors. Data is stored in or retrieved from one or more of the sectors by means of a read/write head mounted on a carriage which is capable of positioning the head at any one of the plurality of tracks.
The disc is rotated at a high speed and the head is simultaneously advanced linearly until the desired sector and track are located adjacent the read/write head, at which point a read/write motor drives the disc at a second speed to allow recording or playback of information at the desired sector or series of consecutive sectors.
Prior random access systems of this type have utilized pneumatic components and mechanical linkages which require an external source of pressurized air. Surge forces, which can produce strong impact forces on coupling members and other components in the system, may be encountered when using pressurized air sources. These strong impact forces can lead to undesirable wear, and can decrease positioning accuracy of the head relative to the disc over the life of the random access system.
Moreover, in random access systems of this type it is difficult to initially calibrate the system so that accurate storage position accessing results, and calibration is difficult to maintain so that the accuracy of this type of prior access system is decreased over the life of the system.
Furthermore, pneumatic drive systems are inconvenient due to the necessity of an external source of pressurized air, and are expensive, noisy and sometimes unreliable.
Also, prior random access units of the type described above suffer from the disadvantage that they are not capable of smoothly linking adjacent tracks in a continuous message. For example, if a message length occupies more than the number of sectors disposed about the disc, such that the head must move from a first track to the next adjacent inner track in order to record or play back an entire message, noticeable disturbances are encountered at the track crossings due to the inability of this type of system to repeatedly follow the same path at these crossings.
A random access system of this type typically utilizes a plurality of serially coupled cylinders for radially positioning the head. Due to mechanical limitations, this type of radial positioning system allows typically a maximum of only four adjacent tracks to be coupled together, thereby limiting the effective length of any message desired to be stored on or retrieved from a disc.